1. Technical Field
The various embodiments disclosed herein relate to low cost high quality LED (Light Emitting Diode) retrofit lamp devices capable to operate in a wide range of power and to supersede conventional lighting devices such as incandescent, halogen, sodium or fluorescent lamps.
More particularly, the disclosed embodiments relate to a LED lamp retrofit apparatus that maximizes the electro-mechanical-optical compatibility of seven interactive systems, such as: 1) Housing, 2) LEDs, 3) LED Panel, 4) Lens/diffuser Shield, 5) LED driver, 6) Supply Adaptor and 7) In/Out Electrical Wiring.
2. Introduction
2.1 Lighting Needs Versus Electrical Energy Resources
According to the data provided by the Energy Information Association (2003, Commercial Buildings Energy consumption Survey, Table E3, FIG. 4), with respect to the commercial buildings in the USA, the ratio of the total electrical energy used for Lighting is 38%, respectively about 3 times larger than the electrical energy used, in the same sector, for the next three large consumers, such as Cooling (13%), Ventilation (13%) and Refrigeration (12%).
Several hundred million dollars and tons of combustive resources are exhausted, yearly, for producing this energy, while experts in ecology warn of global warming and the need for green energy, green products, and energy consumption reduction.
By reducing 4 to 10 times the amount and cost of the energy spent for lighting, the lighting industry may become a minor consumer, even at the country level, while the saved electrical energy could be used more efficiently or more economically, for fulfilling the urgent needs solicited by many other branches of industry.
The solution to achieve this goal already exists: the immediate replacement of all the existing conventional lamps with LED Lamp Retrofits, since the latest developed LED devices have proved to be 5 to 10 times more efficient than the incandescent and halogen bulbs, and more reliable, compact and less polluting light sources than the fluorescent and sodium lamps.
However, the right and complete implementation of these new LED devices will take some time, because of several issues that will be presented below, especially, the particularly issues associated to a potentially possible “Low Cost High Quality LED Lamp Retrofit” ideal device.
The main purpose of all novel solutions disclosed herein is to show that, by maximizing the attributes of each component included in a LED lamp retrofit, while optimizing their each-other compatibility, a heat dissipation and manufacturing cost reduction of 30-60% per unit could be obtained for a high quality device, featuring top specs that none of the conventional lighting device could provide, such as: Efficiency Eff>90%, Power Factor PF>0.99, Harmonic Distortions A.THD<10%, less parts count, low size and weight, high reliability, and minimum five years lifespan.
2.2 Conventional Lamps
The main conventional electrical lighting sources existing in the worldwide market are the incandescent, halogen, sodium, fluorescent and the new introduced LED lamps, each of them having advantages and disadvantages with respect to the others.
A brief functionality study shows that each conventional lamp's physical configuration, operations and performances rely on the interaction and compatibility of seven distinct components, and/or interactive systems, such as: 1) Housing system, 2) Lighting Source system, 3) Mechanical Support system, 4) Lens/diffuser Shield system, 5) Electrical Parameters Control system, 6) Supply Adaptor system and 7) In/Out Electrical Wiring system.
Apparently, some of the conventional electrical lamps existing in the market comprise less than the seven interactive systems mentioned above, because a few of them could be overlapped by the designers for reducing the manufacturing cost and/or for building the lighting device in a more compact fashion.
Nevertheless, by presenting all the lamps existing in the market in the light of the same “seven interactive systems” which are, actually, the main and indispensable components of all conventional lamps, a more accurate and fair comparison could be done in order to reveal properly, the significant advantages provided by the novel LED Lamp Retrofit devices representing the main subjects of this invention.
2.3 Incandescent Lamps
An incandescent lamp or classic Edison bulb represents the first invented electrical device which produces light via a filament heated to a sufficiently high temperature by an electric current passing through it, until it glows.
A conventional incandescent lamp comprises:
A housing system represented by a transparent or translucent balloon made of glass which secures the internal vacuum (no air inside), the lamp internal components' physical integrity versus external corrosive/damaging agents and the electrical shock hazard for the end users.
A lighting source system represented by a filament consisting in a tungsten curly wire which is heated with electrical current up to its incandescence limit (near melting point), for allowing emission of photons (light) omni-directionally (360 degrees angle), outside of the lamp's housing.
A mechanical support system represented by a separate piece of glass or ceramic material supporting the filament via two rigid wires made of still or other electrically conductive material capable to resist at high temperature.
A lens/diffuser shield system represented frequently by the glass balloon housing and for projectors, flash-lighters and other applications, by convergent and/or divergent lens systems incorporated in the glass housing.
An electrical parameters control system represented by an optimized combination of the “internal vacuum” which prevents fast oxidation, the specific recipe of materials included in the composition of the filament, as well as specific dimensions of the curly filament wire's diameter, length or number of turns, which are sized in such a manner to provide maximum light, but simultaneously, to control/limit the lamp's supply current in such a manner for keeping the lighting device's power in the precise range it is designated to operate, despite the anticipated variations of the ambient temperature.
An electrical supply adaptor system represented frequently by a standard “Edison Screw” made of a temperature resistant conductive material which allows the lamp to be easily and safely (i.e. preventing electrical shock hazard) connected to the standard 120 Vac or 240 Vac AC supply fixture.
A two wires in/out electrical wiring system represented by the two rigid wires included in the Lighting Source Mechanical Support system or, by additional flexible wires covered with copper or silver, for achieving an improved conductivity and/or an easier soldering process of connecting the wires with the supply adaptor.
Particularly in/out wiring system may include three or more feed-through terminals or wires embedded in glass. Some devices such as the “three-way light bulbs” have two filaments and three conducting contacts in their bases. The filaments share a common ground, and can be lit separately or together. Common powers include 30-70-100 w, 50-100-150 w, and 100-200-300 w, with the first two numbers referring to the individual filaments, and the third giving the combined wattage.
The incandescent lamp main advantages are: low manufacturing cost, allowance for many different physical shapes, size and AC or DC supply voltage range (1.5 v-300 v), ideal power factor (PF=1), less harmonic distortion (A.THD<5%), natural (similar to the sun's) light emitted Omni-directionally (360°), negligible ultraviolet light exposure, compatibility with triac dimmer control devices and no risk of contaminating the environment with hazardous waste materials such as lead, mercury, or cadmium.
These advantages kept this “Edison bulb” as the #1 source of electrical light, worldwide for over 100 years.
The incandescent lamp's main disadvantages are: low efficiency (1.9-2.6%, typically), low efficacy (12-17 lumens per watt, typically), fragile when mechanical shocks or vibrations occur and very hot (over 100° C. at 100 w), with respect to other lighting devices.
Because of these limitations and/or inconveniences, the incandescent lamps have been replaced in many applications by other types of electric lights, such as halogen, sodium, fluorescent lamps, compact fluorescent lamps (CFL), and recently by light-emitting diodes (LEDs).
“Some jurisdictions, such as the European Union, are in the process of phasing out the use of incandescent light bulbs by banning them with laws to force them being replaced with more energy-efficient lighting.” (Source: Wikipedia—“Incandescent light bulb”.)
2.4 Halogen Lamps
A halogen lamp, also known as a tungsten halogen lamp or quartz iodine lamp is also an incandescent lamp which does not use vacuum for delaying the filament oxidation, but a small amount of a halogen such as iodine or bromine added which, combined with the tungsten filament produces a halogen cycle chemical reaction that re-deposits evaporated tungsten back on the filament, prolonging its lifespan and keeping the envelope clear.
This process allows the halogen lamp to operate at a higher temperature than a standard gas-filled lamp of similar power and lifespan, generating more light in the visible spectrum.
The halogen lamp comprises the same “seven components and/or interactive systems” as the incandescent lamp with the difference that the “vacuum” is replaced with a “halogen gas” inserted in the glass housing, for increasing the light intensity and the filament's lifespan.
A particularly case is the flood halogen lamp which has the housing covered, internally, with a silvery coating (mirror), focusing the light in only one direction, in an angle of about 120 degrees, via a transparent or milky frontal lens/diffuser.
The advantages of the halogen lamps are similar to those of the incandescent lamp, featuring a higher efficiency (2.6-3.5%) and efficacy (18-24 lumens/watt) than the incandescent lamp and additionally, their smaller size at higher power range, permits their use in more compact optical systems for high brightness projectors and illumination, which make them to be a preferred lighting sources at hotels, theaters, casinos, aircraft, watercrafts, and automobiles.
The main disadvantages of the halogen lamp are also similar to those of the incandescent lamp and, in addition, the halogen lamps generate more heat and ultraviolet radiation, requiring some specialized coating of the glass housing for decreasing the level of this radiation down to a non-dangerous level, for the end user.
“Halogen lamps were used on the Times Square Ball from 1999 to 2006. However, from 2007 onwards, the halogen lamps were replaced with LED lights. The year numerals that light up when the ball reaches the bottom used halogen lighting for the last time for the 2009 ball drop. It was announced on the Times Square website that the year numerals for the 2010 ball drop would use LED lights.” (Source: Wikipedia—Halogen lamp.)
2.5 Sodium-Vapor Lamps
A sodium-vapor lamp is a gas-discharge lamp that uses low pressure sodium (LPS) or high pleasure sodium (HPS) techniques to generate light.
LPS are the most efficient light sources so far, having an outer glass vacuum envelope around the inner discharge tube for thermal insulation, but their specific yellow light appearance limits their application to outdoor lighting such as street lamps and parking lots.
HPS have a larger light spectrum but lower efficiency and poorer depiction than other lamps.
The main advantages of the sodium-vapor lamps are: very high efficiency (22-30%) and efficacy (150-200 lumens/watt), as well as the ability to work at very high power range (400 W-1 kW).
The main disadvantages of the sodium-vapor lamps are: the yellow light limiting their use only to outdoor applications, long warm-up/start-up time (several minutes), need of a ballast device (some bulb types), large size, large heat dissipation, fragility versus mechanical shocks or vibrations, and higher manufacturing cost.
The sodium lamps “yellow light” change, noticeably, the original color of objects around (i.e. a red car appears orange, under this light), however, for cities having astronomical observatories around (such as San Jose, Calif.), this light is the ideal one, because it could be easily blocked by selected filters matched with the halogen lamps yellowish light spectrum, with the purpose of getting a darker sky and, implicitly, a brighter stars view.
Nevertheless, now the ultra bright LEDs can do the same job, if necessary, featuring a more accurate control of their light emission spectrum (or color temperature) for increasing the astronomical observatories filters' efficiency, and not necessarily just in the yellow light spectrum but in a different one, offering a more natural light.
At this time the LPS are still the most efficient sources of light existing in the market, since the LEDs typical efficacy is about 100 lumens per watt.
However, besides the fact that the research for ultra bright LEDs just started a few years ago, and new improvements are announced, worldwide, almost on monthly basis (at the “experimental level there are already LEDs exciding 220 lumens per watt), all the other features of the LEDs, such as: longer lifetime, lower manufacturing cost, more compact and robustness versus vibrations, lower size and heat dissipation, no need of ballast, instant start-up, accurate control of the light spectrum, and possibility to reach 2-3 kW power without increasing the device temperature, are sufficient advantages of the LED lamps retrofit for making the sodium ones obsolete. (Source: Wikipedia—Sodium-vapor lamp.)
The sodium-vapor lamp comprises the same “seven components and/or interactive systems” as the previously described lamps, where:
a) the Housing and the Lens/diffuser Shield system could be overlapped in a large and oval glass balloon,
b) the balloon is filled not with halogen but sodium-vapor, component which represents the lighting source system of this lamp,
c) the supply adaptor system and the mechanical support system (3) have different configurations, suitable for the high power street or parking lot lighting
d) the in/out electrical wiring system comprises more than two wires, since this lighting device operations requires a relatively complex external circuit.
e) the electrical parameters control system is located outside of the lamp's housing, consisting in a sophisticated “transformer-ballast” circuitry that provides the long warm-up/start-up time in order to control/limit the lamp's supply current in such a manner for keeping the lighting device's power in the precise range it is designated to operate, despite the anticipated variations of the ambient temperature in winter or summer time.
2.6 Fluorescent Lamps
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapors in the presence of an inert gas, for producing ultraviolet light which causes the fluorescence of a phosphor coating placed internally, and implicitly, light in the visible spectrum.
The fluorescent lamp comprises the same “seven components and/or interactive systems” as the previously described lamps, where:
a) the housing and the Lens/diffuser Shield system are overlapped in a long glass tube internally coated with a translucent phosphorous substance,
b) the tube is filled not with halogen but neon, gas which represents the Lighting Source system similar to the sodium-vapor lamp,
c) the filament used only for the ignition (start lighting) of the gas is split in two sections (ignition filaments) connected separately with a supply adaptor system comprising two plastic caps covering each end of the glass tube and acting also as a mechanical support system (3) for the two ignition filaments,
d) the In/Out Electrical Wiring system comprises four wires coupling each ignition filament with two metallic connectors located on each plastic cap, which are built positioned and sized in such a manner to be operatively connected with a standard (Philips) AC supply fixture, mechanically and electrically.
e) the electrical parameters control system is also located outside of the lamp's housing, consisting in two extra devices:                a “starter”, which is typically a passive components voltage controlled switch, which automatically turns “ON” when the voltage across its terminals is higher than a pre-established threshold amount, and “OFF” when the voltage across its terminals is lower than another pre-established threshold amount, and        a “ballast” which is typically a large impedance coil used for securing the lamp's supply current parameter limitation in a precise range suitable to the specific power the lamp has been designated to operate.        
The standard (Philips) fixture supplies the florescent lighting system with 120 Vac or 240 Vac via two separate circuits: a first circuit including one terminal of the first filament, the ballast, the starter and one terminal of the second filament, coupled in series, and a second circuit including the starter, coupled in series with the two remained terminals of the filaments.
Simply presented, when a high AC voltage (100-240 Vac) source is applied to the fluorescent lamp four terminals, the starter switch is turned “ON” for a short time, closing the two filaments AC circuit, the filaments get warm providing the necessary means to trigger the “ignition”, for the gas inside the lamp to become conductive and to absorb from the AC voltage source as much current as the ballast, coupled in series with the other two terminals of the filaments, would allow. For example, if the AC voltage is 120V and the fluorescent lamp power is 60 W, the ballast impedance must be calculated to limit the current at I=P/V=60/120=0.5 A.
Immediately after the lamp's ignition is established, the voltage across the starter decreases, and the starter switch turns “OFF”, disconnecting the filaments circuit from the AC voltage source. As soon as the neon gas is “conductive”, absorbing a limited current from the AC source, there is no more need for the starter's switch to be “ON”.
In other words, for producing the ignition, the starter may switch ON-OFF for several times, closing and interrupting the ballast AC circuit, via the two filaments, the ballast (inductor) will generate very high voltage auto-induction spikes (over 1 kV, with no “load”) at each time when the starter's switches “OFF” (current interruptions) and the lamp does not absorb any current from the AC source. Eventually, after several ON-OFF cycles, the neon gas in the lamp reaches its ignition, and a 0.5 A current is crossing the lamp, with no more interruptions, so the ballast does not generates any more high voltage spikes (the lamp becomes a 60 W “load”), and the starter remains in its OFF state until the next time when the lamp is disconnected and re-connected to the AC voltage source.
Since over 30 years, many companies around the world, including Philips, General Electric, and Osram-Sylvania have been supplying fluorescent lamps and their adequate fixtures having standard sizes, AC supply adaptors sockets, and complete wiring circuits for allowing easy interchangeability of lamps, ballasts, and starters, for several different power ranges.
A particular florescent lamp is the CFL (Compact Fluorescent Lamp) which uses a smaller diameter glass tube housing, following a spiral shaped (known as the “curly bulb”) which, being designed to replace conventional incandescent lamps, is connected to the power line via a standard Edison screw AC supply adaptor.
The fluorescent lamps main advantages over the incandescent and halogen lamps are: higher efficiency (9-11%), higher efficacy (50-100 lumens/watt) and implicitly, less heat dissipation.
These advantages were sufficient to have made the fluorescent lamps the most used source of light for indoor applications such as commercial buildings, business offices and industrial workplaces.
The fluorescent lamp has many disadvantages, such as: higher cost for the entire lighting system (including the lamp, ballast, starter, and the AC supply fixture), low power factor (0.5-0.7) which requires power factor correction circuits, high level of harmonic distortions (A.THD 60-120%), causing unpleasant radio interference, shorter lifespan if there are switched ON-OFF frequently, longer start-up time (1-3 seconds), ultraviolet emission, lower efficiency or malfunction if the ambient temperature is too high (35-60° C.) or too low (below 0*C) with respect to the standard room temperature (24° C.), relatively large size or complex shape, flickering (stroboscopic effect), incompatibility with triac dimmers and disposal/recycling problems, due to the toxic substances, such as phosphor and mercury, used in their ignition and light emission process.
Because of these inconveniences, the fluorescent lamps are gradually being replaced with more reliable, efficient, compact and less polluting devices, such as LED Lamps. (Source: Wikipedia—“Fluorescent Lamp”, “Compact Fluorescent Lamp”.)
2.7 LED Lamps
An LED lamp (or LED light bulb) is a solid-state (semiconductor) lamp that uses light-emitting diodes (LEDs) as light sources.
The LEDs are small, compact and very efficient lighting devices which, connected in series or parallel circuits (stripes or columns), can provide visible light in a wide range of power, from 50 mW to over 1 kW.
The LED lamps are complex devices capable of reaching higher performances than all the conventional lamps if each of their main components, especially the LED driver circuit, is properly chosen and specifically designed to solve the main inconveniences of only one specific conventional lamp, existing currently in the market.
The most crucial parameters such as: lifespan, efficiency, power factor, harmonic distortions, dimming factor, utilization factor and flickering depend, almost exclusively, on the LED driver circuit's configuration and electrical performances. In various embodiments, the present specification provides “LED Drivers” in an “LED Lamp Retrofit”, for example.
Because, the LED lamp retrofits and implicitly, their LED driver circuit represent the main subjects of this specification, and a fair comparative presentation of a specific LED lamp advantages, versus conventional lamps and/or other LED lamps, requires a very complex market analysis study, a detailed description of several conventional “LED lamp retrofits” and “LED Lamp Drivers” will be presented hereinbelow.
3. LED Lamp Retrofits
By definition, a “lamp retrofit”, device must have similar physical aspect, light distribution, brightness, size and supply adaptor connections as each specific conventional lamp subject of replacement.
Since in the worldwide market there are already hundred kinds of different incandescent, halogen, sodium and fluorescent lamps operating in a 1 W-1 kW power range having different size and shape, from a few feet long tube fluorescent lamp down to a quarter of an inch diameter spherical flash lighter's bulb, obviously it cannot be only “one LED lamp retrofit” replacing, alone, all the existing conventional lamps.
Therefore the LED lamp retrofit, subject of this invention, comprises the same “seven components and/or interactive systems” as all the other previously described lamps, however, having enough versatility to be able to follow each conventional lamp particularities, as follows:
A housing system which, from case to case, it could be a transparent or translucent balloon or tube made of glass or plastic, for securing the lamp internal components' physical integrity versus external corrosive/damaging agents and for preventing potential electrical shock hazard of the end users.
A lighting source system represented by one or more LEDs for converting the electrical energy in photons (light).
A mechanical support system represented by an LED panel which, from case to case may have a disc, square or rectangular configuration when the light has to be dispersed in an angle no larger than 180 degrees, or a tri-dimensional prism shape when the light has to be dispersed omni-directionally (360 degrees angle), outside of the lamp's housing.
A lens/diffuser shield system which, from case to case, it could be overlapped with the housing, it could be discretely attached to each LED device, or it could be represented by a separate convergent and/or divergent optical system attached to the housing and appearing as a transparent, translucent or monochromatic lens.
An electrical parameters control system represented by an SMPS (switching mode power supply) or monolithic (solid states) LED driver circuit which, from case to case, it could be operatively connected to each LED device, or to a LED stripe circuit, or to a LED array circuit, or to all LEDs of the lamp retrofit connected operatively, in series and/or parallel sub-circuits (stripes).
An electrical supply adaptor system which, from case to case, it could be a two connections standard “Edison screw” adaptor, or a four connections standard (Philips) AC fixture adaptor, or any other adaptor which allows the lamp to be easily and safely (i.e. preventing electrical shock hazard) connected to the standard 120 Vac-240 Vac supply line, or to any other higher or lower AC/DC power sources.
An in/out electrical wiring system which, from case to case, it can be represented by just two or more supply wires, or it could be an “intelligent in/out wiring system” comprising temperature or motion sensors and/or any other device capable to improve the lamp retrofit operations' performance and safety.
Over the last five years, the LED lamp retrofits are successfully replacing almost all the conventional lighting devices and governments of developed countries are encouraging and supporting this action.
The main issue associated to these LED lamp retrofits immediate replacement of the conventional lamps is the higher cost per unit, an inconvenience which could be compensated if the retrofits' lifetime can be sufficiently extended (5-10 years) for end users to be able to recover the extra cost from the monthly savings in the electrical utility bill.
Unfortunately, because the LED lamp retrofits comprise LED driver circuits, which include unreliable and bulky parts such as high voltage electrolytic capacitors and oscillating coils, the lifetime of these retrofits could be estimated, conservatively, up to about two years, a fact which forces the manufacturers to guarantee 5 years lifetime of their product only if the product is not used more than 4-8 hours a day.
Therefore now, most of the worldwide power management companies are doing their best efforts to solve these issues, either by decreasing the retrofits cost per unit down to the same cost as the conventional lamp replaced, which could be considered “the economical marketing strategy”, or by prolonging, sufficiently, the lifespan of the LED lamp retrofits, for justifying their extra cost, which cold be considered “the high tech marketing strategy”.
3.1 Implementation
A good quality LED lamp retrofit should replace, easily and operatively, each conventional lamp, matching, as closed as possible the physical dimensions, electrical supply adaptor, light intensity and light quality of the conventional lamp it is designed to replace.
Additionally, the recently introduced “smart control systems” require, or will require, more complex lighting systems having the capability to allow control via computers, in a “remote feedback” manner, in which each Lamp retrofit provides data (obtained via sensors) about its momentarily status in its particularly environment, for parameters such as temperature, humidity, outdoor light, motion in vicinity, current consumption versus light intensity, than the computer controls each node or lamp, accordingly, in an “ON-OFF Mode”, for a better distribution of light and for avoiding “overheating” in some areas, or in a “Dimming Mode” for adjusting, properly, the light intensity and/or color, in other areas.
Such a smart control system implementation is possible and not to difficult to be achieved now, more than ever before, since all LED lamp retrofits include electronic driver boards, for controlling the LED current despite large variations of the supply voltage and ambient temperature, and since the cost of the digital parts used in I/O data communications have decreased dramatically, over the last ten years, the upgraded lamp retrofits cost per unit will not increase, significantly, if a “remote feedback” circuit will be included in a “smart LED driver” board and an “I/O data wiring connectors system”, or “wireless communication system” would be added to a “smart LED lamp retrofit” device, for “remote feedback” purposes. In various embodiments, for example, the present specification provides remote control and feedback in an LED lamp retrofit as described in connection with FIG. 20, which includes a micro-controller and temperature sensor.
Since the low cost per unit is a mandatory demand of the large volume markets and an important subject of this specification as well, the following description of each LED Lamp retrofit will include references related to the cost associated to the manufacture and/or operations process of each particularly lamp retrofit.
In this light, features such High Efficiency, High Efficacy and High Power Factor represent not just “state of the art” attributes, but also economic advantages associated to each particularly LED lamp retrofit, since a “Near Unity Power Factor Long Life Low Cost LED Lamp Retrofit” could save an amount of money equivalent to more than times its total cost, by considering the 50-90% of electrical energy saved over ten years (or over 100,000 hours non-stop operation), versus the $0.15 cost per kilowatt, saved for each hour of operation.
In other words, over at least five years time period, an end user will get full return and additional cash profit for each LED lamp retrofit purchased, even the retrofit's costs is now 3-5 times more expensive than the conventional lamps, operating in the same power range.
With respect to the electrical energy utility bill, everybody know that a highly efficient lamp saves money, because as long as the electricity meter (counter) shows less amount of kWh (kilo-watt-hours), for the same light quality and period of time, obviously the utility (PG&E) bill will be less expensive. However, not too many end users know that, since a few years ago when PG&E has introduced its “smart meters”, the electrical utility bill has been substantially increased (up to 40% for consumers having PF=0.6) for “Low Power Factor Electrical Devices” so from now on, only the “Near Unity Power Factor” devices will have the benefit of “no extra charge”, in the monthly electrical utility bill.
This new way of billing the consumers of electricity in California has been already confirmed by the Pacific Gas & Electric (PG&E) in an internet educational publication:
“Power factor adjustment is calculated for larger customers, over 400 kW, to appropriately charge for the larger percentage of reactive power used. At PG&E we average the power factor over the entire monthly billing period.” (http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/understanding.pdf)
This apparent “overcharge” is totally fair, since for each electrical device absorbing 60 W power, under a power factor coefficient of 0.6, the utility (PG&E) has to deliver 100 VA “reactive power”, even the difference of 40 VA is not used by the end user, but is converted in “overheat” by the utility provider's high power transformers, relays and wiring systems.
The best solution to solve these issues is to include a PFC sub-circuit in each LED lamp retrofit's driver circuit, in such a manner for the size and cost of the upgraded driver to not increase considerably.
Accordingly, all the LED driver novel solutions presented in this patent application allow for near unity (0.95-0.99) power factor LED lamp retrofits, in which the PFC sub-circuit's cost is less than 5% of the entire lamp's cost, featuring less parts count and size, as well.
3.2 Incandescent Lamp Retrofit
An incandescent lamp retrofit, as discussed hereinbelow in connection with the embodiment shown in FIG. 1, for example, should provide its light omni-directionally (360 degrees angle) in a range of power from 2 W (5-10 W conventional luminaries replacement) to 10 watts (40-100 W conventional Edison bulb replacement), it is supposed to have the same supply socket or the same size “Edison Screw” AC supply adaptor and the same physical shape a for being able to replace, easily and operatively, any conventional incandescent bulb.
The US Department Of Energy (DOE) recommended a minimum power factor of 0.7 for the lamp retrofits used in residential areas and a minimum 0.9 power factor for the business and industrial lighting section.
However since, on one hand, the low power LED lamp retrofits' parts total cost is more expensive than the cost of a “tungsten filament” and, on the other hand the internal space available in this low size bulb is too small for allowing the use of high quality LED driver circuits, most of the large volume manufacturers, such as Phillips, GE, Lights of America and others have already introduced in the market thousands of LED lamp retrofits having a very poor power factor (0.5-0.75).
Good reputation semiconductor companies, such as TI, Philips, Power Integrations, Linear Technology, iWatt, ONSEMI, Fairchild are advertising new LED driver circuit solutions featuring a power factor over 0.9 on monthly basis, since over three years ago, however, either because this solution is still too expensive at this time and/or because the size of the driver circuits is too large to fit in the limited available space inside of the lamp, none of these solutions are used currently, by the large volume LED lamp retrofit manufacturers.
3.3 Halogen (Flood) Lamp Retrofit
A halogen flood lamp retrofit, as discussed hereinbelow in connection with the embodiment shown in FIG. 2, for example, should be larger in size for operating in a 10-14 Watts power range, having the same “Edison Screw” AC supply adaptor and it is supposed to focus its light in only one direction (flood), under an angle of about 120 degrees.
The LED lamp retrofits for larger power halogen bulbs have sufficient internal available space for adding a PFC board, however, by considering the low cost of the existing halogen bulbs, it is almost impossible for the large volume manufacturers to build high quality lamp retrofits, at a competitive cost per unit, unless the LEDs and/or the LED driver boards cost decreases, considerably.
3.4 Fluorescent Lamp Retrofit
A fluorescent lamp retrofit, as discussed hereinbelow in connection with the embodiment shown in FIG. 3, for example, should follow a tube shape having, precisely, the size as and the same conventional two connectors AC supply adaptor coupled, symmetrically, at both ends of the lamp, in order to match with the Phillips, GE and Sylvania standard supply fixture and to operate in a 16-24 watts power range for reaching at least the same light intensity as a 60-80 watts fluorescent lamps.
For this particular retrofit, the LED lamp has significant advantages, consisting in the fact that the fluorescent lamp light angle is 360°, however, these lamps' fixtures are mounted against the wall, so almost 50% of its lighting capacity is wasted, unless good quality mirrors (reflectors) are included in the fixture, for guiding the light back, in the right direction. The LEDs 120 degrees light angle allows this kind of retrofit to reach the same light intensity and better quality (sun light), guided on the right direction, and with just 15 W power consumption to replace a 60 W conventional fluorescent lamp, without using large and expensive bright white fixtures or reflectors, as discussed hereinbelow in connection with the LED lamp retrofit embodiment associated with an LED panel for a T8 retrofit.
An additional advantage of this particular retrofit consists in the fact that the size and cost of the replaced lamp (including its large and expensive fixture, ballast and starter) allow for a “higher performance higher cost” LED lamp, but unfortunately, still most of the new T8 fluorescent LED lamp retrofits, existing in the market, have the power factor less than 0.9 (some of them even less than 0.7), because of the extra cost and extra size of the driver board, required by a PFC circuit comprising 15-30 parts, typically.
3.5 Other Lamps Retrofits
Other LED lamp retrofits, as discussed hereinbelow in connection with the embodiment shown in FIG. 4, for example, could be designated to replace very small bulbs, large street lighting sodium lamps or huge lighting panels, accordingly in such applications it is recommendable for the LED lamp retrofit to be designed as a “compact light engine” unit, respectively, to have a spherical or cubical monolithic configuration which allows for many units to be connected next to each other, in series and/or parallel circuits, similar to the conventional lighting panels using hundreds of incandescent bulbs.
Ideally, a “compact light engine” should include only two parts, respectively an LED Array module and a silicon microchip, coupled directly to the LEDs.
Some “pioneers” in the worldwide industry, such as Exclara, Supertex, Seoul Semiconductor and a few others have introduced a new technology that eliminates the need for capacitors and coils used in the “conventional LED drivers” and allows for “Monolithic LED Driver” (fully integrated) solutions, near unity power factor and over 90% efficiency.
This new technology could be the key to “the right solution” for a very low cost, but also very high quality, LED lamp retrofit.
Accordingly, the present specification provides several novel solutions for upgrading incandescent, halogen, sodium and fluorescent LED lamp retrofits, comprising conventional LED drivers, as well as monolithic LED drivers.
4. LED Lamps Retrofits Main Components
For a fair and easier quality versus cost comparison between all lighting devices presented in the present specification it would be considered that, similar to the embodiments presented herein, all LED lamp retrofits existing in the market comprise the same seven main components, such as: LEDs, LED Panel, Supply Adaptor System, Housing, Lens/diffuser Shield, LED Driver, and LED driver's In/Out Electrical Wiring System, regardless of the fact that some of the lamps may appear to have fewer components, because two or more parts are integrated into one component capable of performing, simultaneously, 2-3 functions required by a particular LED lamp retrofit's lighting operations.
The LED lamp retrofits performances quality and operation lifetime depend on the physical configuration, electrical characteristics, reliability and lifespan of each of its components, as well as on the capability of these components to match each other, for optimizing the quality versus cost feature of each particularly lamp retrofit.
4.1 LEDs and LED Arrays
The LEDs are basically mono-chromatic Light Emitting Diodes or nonlinear semiconductor devices introduced in the industry since over thirty years ago as “tiny monochromatic lighting sources” capable of generating just a few colors, such as Red (or Infrared), Green, Yellow and Orange used, mostly, in display panels for electronic equipment, stereos, toys, infrared remote control and other low power lighting applications.
Because of their small power consumption (20-100 mW) and low cost, there was no need for a “high efficiency high power factor LED drivers”, at that time, since even a low power/low cost operational amplifier could supply an LED in a “constant voltage constant current” manner, securing the circuit lifespan for a period of 10-20 years.
During the last decade, shortly after the blue LED was finally created, the applications field of these devices has increased dramatically, because by combining, in whatever ratio, the Red, Green and Blue (“RGB”) colors, any other “specific color” of the visible spectrum (from Infrared to Ultraviolet, including “White”) could be easily obtained, offering the necessary means for the high efficiency “color video display” used now in small and ultra large TV/Monitors/Advertising video screens, as discussed hereinbelow in connection with the embodiments for RGB type LED lamp retrofits, for example.
Over the last five years, the “Ultra Bright White LED” technology, developed from the blue LED technology, has been rapidly developed by high volume manufacturers such as CREE, Lumileds, Nichia, and many others, offering a large diversity of LED devices operating in a range of power from 50 mW to over 5 W per unit, which can be easily connected in series and/or parallel circuits (similar to the conventional diodes matrix circuits) and used in low power (1-50 W), as well as in high power (100 W-1 kW) LED lamp retrofits, absorbing 5-10 W less electrical energy than incandescent or halogen lamps, from the AC power grid, for similar lighting power.
At this range of power and especially, for such serious applications such as aircrafts, watercrafts, street and commercial lighting systems, obviously a low power and cost operational amplifier cannot secure the job, so there is an urgent need for more complex “high reliability, high performance, long lifetime LED lamp” driver circuits, capable to operate in a range of power from 1 W to 1 kW.
The 50 mW LEDs require a constant current of maximum 20 mA and their cost per unit is very low now, after the apparition of the higher current (100 mA to 5 A) LEDs which offer the advantage of using less number of LEDs for any given power of a LED lamp retrofit. In the same range of power, the cost of 100 LEDs of 50 mW power each is now lower than 5 LEDs of 1 W power each, but because five LEDs could be connected in only one stripe having its current secured by only one constant current sink device, while the 100 small power LEDs may need 20 constant current sink devices (in the same configuration of 5 LEDs per stripe), most of designers prefer to use the more expensive higher power five LEDs. South Asian manufacturers prefer the low cost low power LEDs, using hundreds of them in only one T8 fluorescent retrofit lamp, connected in 20-30 stripes and using low cost ballast resistors, per each stripe, instead of constant current sink devices. This solution is good only for reducing the retrofit cost per unit, however, the chances for these kind of lamps to last more than two years are very low, as discussed hereinbelow in connection with the embodiment shown in FIG. 24, for example.
Many LEDs manufacturers now offer the so called “LED Array”, “6V LED”, “20V LED” or “50V LED” which are, actually, two, six, fifteen or more LEDs mounted, very close to each other on a thin aluminum board, then connected to each other in series and/or parallel circuits using a very productive and cost effective technology that allows printed circuits deposited on an “aluminum oxide” substrate which solved, simultaneously, the heat transfer and the electrical isolation issues associated to the manufacturing process of LED lamp retrofits using more than one LED, as discussed, for example, hereinbelow in connection with the embodiments shown in FIGS. 4 and 20.
The LEDs main advantages over the conventional lamps are: more compact, smaller size and weight, higher efficiency, higher efficacy, less heat dissipation, highly resistant to mechanical shocks and vibrations, longer lifespan, precisely controlled light spectrum, no ultraviolet or x-Ray radiations and no disposal/recycling problems.
The main inconvenience associated to the LED's behavior is the nonlinearity aspect, associated to the fact that typically, an LED absorbs almost no current when the voltage across its terminals increases from 0V up to about 2.8V, than it starts absorbing rapidly, more and more current when the voltage increases between 2.8V and 3.3V supply and finally, the LED may me be exposed to irreversible damages (or simply it may “blow up”) if the LED's current increases above its recommended limit, even by increasing the voltage (and not limiting, somehow, the LED's current) with just 0.1-0.2 volts.
Additional inconveniences consists of the fact that the LEDs require rectified AC current which calls for a relatively sophisticated and expensive power factor correction circuit, the LEDs current amount changes, considerably, with ambient temperature variations, when coupled in parallel stripes the LEDs need a ballast resistor or a constant current sink for balancing the current per each stripe, they lose completely the light at any time when the voltage across a LED stripe is only a few fractions of a volt lower than the typical multiple of 2.8V-3.3V threshold, creating an irritating “flickering” effect, especially when dimmers are used.
In conclusion, the LEDs have a strong potential to be the future ideal lighting source which will replace, eventually, all the conventional lamps existing around, however, because of several inconveniences, these amazingly compact and efficient devices cannot perform as well as expected from an efficient and reliable lamp retrofit without having “full match” with each and all the other six components, discussed hereinbelow, in various example combinations and permutationsf.
4.2 LED Panels
The LED panels are, basically, the mechanical support for one or more LEDs connected in any series or parallel circuit combination offering the optimum implementation or maximum brightness with respect to the lamp's physical configuration, available internal space, light direction, dimming capability and uniform light distribution of each specific LED panel included in a specific LED lamp retrofit.
The LED panel configuration and the electrical connection between the LEDs have to be designed in such a manner for providing maximum brightness by using or not using a reflecting mirror and, also, the light has to be symmetrically distributed on the entire LED panel surface, even a dimmer reduces the maxim supply voltage, switching “off”, one after the other, all the LEDs stripes, as the maximum supply voltage decreases.
Four main LED panel configurations are currently used, or could be used, such as:
a) a three dimensional LED panels for incandescent LED lamp retrofits, which has to secure an Omni-directional light and a symmetrically distributed light in case the amplitude of the supply peak decreases, as discussed hereinbelow in connection with the embodiments shown in FIGS. 5 and 6, for example,
b) a flat disk LED panels for halogen (flood) LED Lamp retrofits, as discussed hereinbelow in connection with the embodiment shown in FIG. 2, for example, which provides a spot light and a symmetrically distributed light in case the amplitude of the peak input voltage decreases, as discussed hereinbelow in connection with the embodiment shown in FIG. 6, for example,
c) a flat rectangular LED panels for fluorescent LED Lamp retrofits, as discussed hereinbelow in connection with the embodiment shown in FIG. 3, for example, which provides uniform light over a several feet long transparent tube and where the light has to remain symmetrically distributed in case the amplitude of the supply peak voltage decreases, as discussed hereinbelow in connection with the embodiment shown in FIG. 5, for example, and
d) a flat miniature LED Array for monolithic light engine LED lamp retrofits, as discussed hereinbelow in connection with the embodiment shown in FIG. 4, for example, which provides a uniform and symmetrically distributed light in case the amplitude of the supply voltage decreases, as discussed hereinbelow in connection with the embodiment shown in FIG. 7, for example.
4.3 Supply Adaptors
For any lamp retrofit, the supply adaptor is a component, which allows the end user to replace, shortly and operatively, the obsolete conventional lamp used until the day of replacement, without any need to employ an authorized electrician and/or to take the risk of doing “improvisation” in order to connect the new lamp to the dangerous high voltage electrical power grid's standard terminal.
Therefore, most of the LED lamp retrofits are equipped with exactly the same supply adaptor, described above, for each standard power and size incandescent, halogen, sodium, and fluorescent lamp, subject of the replacement.
4.4 Housings
The LED lamps retrofits' housings have significant economical advantages, with respect to the conventional lamps' housing, because since the LEDs do not need vacuum or rare gases for producing light, there is also no need for the housing to be made from glass, which is heavier, more fragile and more expensive than plastic or aluminum.
The housing provides mechanical support and environmental protection (against raining, humidity or dust) for all the other components of the retrofit lamp, and it could appear as a transparent plastic globe which replace also the lens/diffuser shield, or it could be made from aluminum and used also as LED panel and as heat sink for cooling down the LEDs operation temperature and keeping them highly efficient.
In case the housing is made from aluminum, or any other metal, serious precautions have to be taken, making sure there is a 2 kV-4 kV isolator material between the housing and any electrical component (LEDs, LED panel, LED driver, supply adaptor, wiring supply circuit) coupled, directly, to the AC power grid, for protecting the end users against electrical shock hazard, as discussed hereinbelow in connection with the embodiments of non-isolated drivers, such as a monolithic driver, for example.
4.5 Lens/Diffuser Shields
The lens/diffuser shields of the existing LED lamp retrofits have different size, shape and transparence grade (transparent, translucent, milky, color filter, magnifying glass stripes, etc.) following, as close as possible, the exact appearance of the conventional lamp subject of replacement, in order to provide at least the same intensity, quality and spectrum of light to many end users which, for different reasons, may have strong preference for a specific lamp type.
Some of the LEDs, existing in the market, come with a small magnifying lens incorporated into their plastic package, which increase their brightness but decrease their light cone's angle, down to about 90°.
For outdoor applications, the lens/diffuser shield device has to be hermetically (water proof) coupled to the housing of a LED lamp retrofit, for securing the lamp's high reliability versus rain, dust or any other adverse factor able to damage the LED lamp retrofit's circuit.
4.6 In/Out Electrical Wiring System.
The LED driver's in/out electrical wiring system comprise three main circuits, such as:
a driver supply circuit, which consists of two or more wires coupled with a DC source such as a car battery, a high voltage AC source such as the 120V-240V power grid, or to a 50-60 Hz power transformer.
a LED supply circuit, which may also include two or more wires, in accordance with the configuration of the LED driver and the LED panel circuits.
a remote feedback wiring circuit, comprising two or more wires coupled between the LED driver circuit, which should include sensors and a microcontroller system capable of exchanging in/out data, and an “in/out data connector” which connects the LED lamp retrofit with an external computer system or directly to the internet.
Currently, there are already available “smart remote control circuits” via which end users can switch on/off or even dim all lights in their apartment, via internet, even during a trip out of the country.
4.7 LED Drivers
Currently, there are hundreds of different LED driver circuit configurations available on the worldwide market, each of them following different circuit topologies and offering different advantages, such as: lower cost, smaller size, less parts count, higher efficiency, higher power factor, less harmonics (noise), off line (90-240 Vac supply range) capabilities, wide range dimming capabilities, however, each of them having some limitations or inconveniences, as well.
Very generically, these devices could be separated in two main groups such as: a) ballast LED drivers, b) Switching Mode Power Supply (SMPS) LED drivers, and c) Monolithic LED Drivers, all of them being capable to operate as DC/DC or AC/DC LED diver circuits, if a bridge rectifier is performing the AC/DC conversion.
The ballast LED drivers are the most simple and cost effective ones, consisting of just a resistor or a simple constant current sink (CCS) circuit coupled in series with one or more LEDs.
The SMPS LED drivers are now the most used devices in the LED lighting industry, following the conventional (over 30 years old) Pulse Width Modulation (PWM) converter control method, based on the coils and capacitors capability of storing electrical energy, being currently promoted in the worldwide market by all major power management companies, such as TI, Phillips, Maxim, ST Micro, Toshiba, Fairchild, ONSEMI, Power Integrations, Semtech, Linear Technology, and many others.
The Monolithic LED drivers provide a unique controlling method which eliminates the need for coils and capacitor and allows for a very compact and cost effective fully integrated driver circuit solution, being introduced in the market recently, by several “pioneers” in the industry, such as Exclara, Seul Semiconductor, Samsung, Supertex and a few other companies.
Since each of the three controlling methods mentioned above allows for many different circuit topology applications having advantages, but also inconveniences with respect to each-other and the SMPS LED drivers, as well as the Monolithic LED drivers are, both, important subjects of the present specification, detailed description of several LED driver circuit solutions, promoted in the market by very good reputation power management companies, will be presented hereinbelow.
5. Simple Ballast LED Driver Circuits
5.1 Resistor Ballast LED Driver
In low power range and regulated (constant) voltage DC/DC applications, a LED Driver circuit working at room temperature (23°-25° C.) could be extremely simple and cost effective, consisting of just “one resistor” (costing less than $0.01) coupled in series with a LED, or a LEDs stripe, as a “ballast circuit”, for limiting the LED's current down to a safe amount, representing typically, no more than 80% of the LED's maximum ratings specs, for securing “safe margins” versus the LEDs current/voltage specs variation, from unit to unit (LED's specs tolerance), and versus small variations of the ambient temperature and/or supply voltage ripples.
As a simple example, in an applications where the supply voltage is obtained from a 12V DC car battery, the voltage per each LED is required to be 3.2V and the maximum average current, Imax, is 20 mA (16 mA as 80% of Imax), the most “simple driver” is a resistor coupled in series with a “stripe” (column of devices coupled in series) of three LEDs requiring 3.2V×3=9.6V where the resistor's value is 12V-9.6V=2.4V/0.016 A=150 Ohms, and the system efficiency is Eff=9.6/12=80%.
For getting “more light”, many stripes of three LEDs having a ballast resistor of about 150 Ohms could be connected in parallel and, in ideal and stable environmental conditions, if the substantially low efficiency of this particular system is ignored, a resistor could be the most simple and low cost driver included in a LED lamp retrofit, designated to replace the conventional incandescent or halogen bulbs used in the automotive industry.
However, in real world situations, the simple solution described above has many disadvantages since it does not protect the LEDs against large variations of the supply voltage (a car battery voltage may vary from 9V to 15V) or ambient temperature (summer vs. winter seasons) and additionally, a significant percent of the supply electrical energy is lost in heat, on the ballast resistors, decreasing the entire LED Lamp retrofit efficiency down to 80%, or less.
Therefore, in order to overcome these shortcomings, there is a need for more complex LED driver circuits capable of maintaining the LED current and voltage within precise pre-established limits, despite large variations of supply voltage and/or ambient temperature, in such a manner for the conversion of the electrical energy in light to reach maximum efficiency.
5.2 Constant Current Sink LED Drivers
The constant Current Sink (“CCS”) drivers, are capable of securing a safe current trough the LED stripe, despite large variation of ambient temperature, however, when the supply voltage increase to an amount significantly higher than the LED stripe's threshold voltage, the difference in the voltage will increase the heat dissipation of the CCS device and implicitly will decrease the driver's efficiency. On the other hand, when the system supply voltage goes lower than the LED stripe's threshold voltage, even for a short period of time (ripples), the entire LED stripe will shut off its light, for that period of time, creating an irritating flickering (stroboscopic) effect.
In conclusion, the CCS devices are useful and strongly recommended only in DC circuits where the supply voltage is reasonably constant (small ripples) and close to the LED stripe's threshold voltage.
Nevertheless, there are already on the market very low cost CCS LED drivers used even in AC circuits (via a bridge rectifier), but their poor efficiency, power factor and A.THD parameters represent a strong barrier for this kind of driver to become the ideal “low cost high performances” LED drivers, on the worldwide market.
6. Switching Mode Power Supply (SMPS) LED Driver
The SMPS LED driver circuits follow conventional Pulse Width Modulation (PWM) boost, buck, buck-boost or flyback transformer converter circuit topologies which include reactive components, capable of storing and converting the electrical energy, such as inductors and capacitors as well as integrated circuits, transistors, diodes and resistors.
The main inconvenience of the SMPS drivers consists of their dependence on bulky and unreliable reactive components, such as oscillating coils and electrolytic capacitors in order to convert and store the electrical energy, as well as filtering coils and high voltage capacitors for their EMI (low pass) filters, which stop the high frequency noise, generated by the SMPS converters, to penetrate the electrical power grid.
At relatively high temperatures, which are expected inside of LED lamp retrofits, the electrolytic capacitors lifespan is relatively short (about 2 years) and also, the high frequency coils or transformers (flyback) isolation and/or magnetic core characteristics could change, dramatically, with the ambient temperature and humidity factors, limiting the lifetime of the entire LED lamp retrofit device down to 2-3 years.
6.1 DC/DC SMPS LED drivers
The DC/DC SMPS LED drivers are capable of overcoming the shortfalls in all the ballast LED drivers, in a conventional manner, by using a PWM converter comprising a controlling circuit (semiconductors), an oscillating inductor (coil) capable to, periodically store and deliver electrical energy, in high frequency constant output voltage pulses, to a load (LEDs), across which there is a capacitor that storage the electrical energy, for keeping the LEDs lighting, without flickering. The modern PWM controller integrated circuits (ICs) can control their output voltage, in such a manner, that even if the system supply voltage goes lower, or ten times higher than the LEDs stripe's threshold voltage, the voltage across the LEDs stripe remains constant, and just a little higher than the LEDs stripe's threshold voltage, for avoiding flicker and maximizing the system's efficiency.
6.2 Constant Voltage Constant Current LED Drivers
The constant Voltage Constant Current (“CVCC”) LED Drivers use both, a PWM converter and a CCS device for securing, at the highest degree, the stability of the LEDs voltage and current parameters and prolonging the LED lamp retrofit's lifespan to the maximum period of time allowed by each component, especially by the unreliable high voltage electrolytic capacitors, included in most of the SMPD LED drivers.
For achieving ultra-reliable CVCC LED driver solutions, a conventional CCS circuit including a MOSFET buffer transistor in feedback with an operational amplifier (OPAM) is recommended to be inserted in series with each LED stripe for securing long term lifespan to the LED lamp retrofit. As good examples both, the MAX16834 LED driver chip provided by Maxim and the LT3756 LED driver chip provided by Linear Technology are capable of offering this state of the art CVCC circuit implementation, by using an additional external MOSFET buffer as CCS, controlled by an internal OPAM, however, this protection is used for only one LED stripe. For more than three stripes, this very reliable OPAM-MOSFET-CCS circuit becomes too expensive and therefore designers prefer to use only one stripe of higher power and more expensive LEDs, rather than cheaper LEDs coupled in more stripes. Accordingly, in various embodiments, the present specification provides a CVCC LED driver as described hereinbelow in connection with FIGS. 8 and 9, for example.
The maximum efficiency of a DC/DC SMPS LED Lamp retrofit depends of the number of LEDs per stripe and the PWM circuit topology used for the LED driver. As more LEDs are connected in series on one stripe, the higher the voltage threshold and, implicitly, the lower the entire circuit's current will be, for the same power range. Lower current means lower heat, which means lower dissipation and higher efficiency. However, the four conventional PWM circuit topologies mentioned above have their own particular advantages and shortcomings, such as:
6.3 Boost Topology
The boost circuit topology allows for the simplest (less parts count), most efficient (Eff=90-95%, typically) and low cost PFC or PWM LED driver implementations, with two main shortcomings:
a) it does not offer isolation between the input and output circuits and
b) its output voltage is always higher than its maximum input voltage.
In relation to the LED driver's case designated for automotive battery LED lamp retrofits supplied with 10-15V as mentioned above, a safe constant output of minimum 17 Vdc of a boost circuit will supply a stripe of 5 LEDs (assuming a 3.2V/LED, 16V/5 LEDs) coupled in series, with only 1V remaining across the driver's buffer. Since the LED current is equal with the CCS buffer current, the “output circuit efficiency” (LEDs—CCS) is, briefly: Eff=16/17=0.94. In case a higher output voltage is chosen, it has to be increased in increments of 3.2V, for adding one, two more LEDs, and keeping the “extra voltage” not higher than 1V with respect to the LED stripe maxim voltage, for maintaining a good efficiency of the system. In high power/high efficiency boost driver systems, that “extra voltage” has to be dropped down to 0.1V (using low value sense resistors techniques), for the entire boost system's efficiency to be around 0.94, since about 5% of the supply energy is dissipated in heat by the boost inductor (coil), the MOSFET switch, the controller IC and the other 15-20 components included in the circuit.
6.4 Buck Topology
The buck circuit topology, which also allows for circuits with fewer component counts, is reasonably efficient (Eff=85-90%, typically) and cost effective, having two main shortcomings:
a) it does not offer isolation between the input and output circuits, but even more, there is a direct current from the high voltage DC source trough the LED stripe to ground which could damage the LEDs if the converter's buffer fails in a “short circuit” fashion and,
b) its output voltage is always lower than its minimum input voltage.
In relation to the LED driver's case designated for automotive battery LED lamp retrofits supplied with 10-15V mentioned above, a safe constant output of maximum 9 Vdc of a buck circuit is too low to supply a 3 LEDs stripe (3×3.2V=9.6V so no LED will light), so in case that a stripe of only 2 LEDs (3.2V×2=6.4 V) is used, the voltage difference will be 9V-6.4V=2.6 V which means a “LED Stripe—CCS output circuit” with an efficiency of just 71%, which is unacceptable.
Therefore in any design, the buck output voltage has to be set as closed as possible to the two LEDs stripe threshold voltage (6.4 V) and, for the same total numbers of LEDs and lighting power of a LED Lamp retrofit, more LED stripes have to be added, fact which will increase the circuit total current and implicitly, the entire system efficiency will decrease.
6.5 Buck-boost Topology
The buck-boost circuit topology overcomes some of the above mentioned shortcomings by allowing higher, equal or lower output voltage with respect to its input supply voltage amount, operating with good efficiency (85-90, typically) and less parts count.
The SEPIC (Single-Ended Primary-Inductor) converter is a particular buck-boost circuit having non-inverted output coupling energy from the input to the output via a series capacitor to a second SEPIC inductor, fact which increase the complexity of the circuit but allows for a “single ground” configuration which eliminate the need for differential or opto-coupler sensing of the current or voltage across the load.
The three main shortcomings of the buck-boost topology are:
a) it does not offer isolation between the input and output circuits,
b) it requires sophisticated differential voltage sensing method of the output V/I parameters (not for SEPIC) because its output circuit has a different zero volts reference with respect to the input circuit,
c) it requires a special “constant Off time” controller IC when it is working in CCM (Continuous Conduction Mode) and an additional power factor correction circuit in AC applications.
6.6 Flyback Topology
The flyback circuit topology is the only circuit which, via its two coils flyback transformer, provides complete isolation between its input and output circuits and allows for higher, equal or lower output voltage with respect to its supply voltage amount.
The flyback circuit shortcomings are: more expensive, more parts count, larger size, lower efficiency (75-85%, typically, 90% using expensive parts), two separate grounds which require a sophisticated differential current/voltage sensing circuit and an additional opto-coupler circuit, in order to control the momentary value of the LED's current and voltage parameters with respect to isolated ground, and to secure the circuit's long term lifespan.
In conclusion, the flyback circuit main advantage is the “full isolation between the input (AC power grid) and the output (LEDs) circuit, fact which make this circuit the most preferred one in situations when a LED lamp retrofit has a “metallic housing” and a risk of electrical shock hazard may exist for the end users.
Nevertheless, most of the worldwide providers of LED lamp retrofits solved this problem by using plastic or glass housing and/or by using a 2 kV-4 kV isolated material inserted between the LEDs (output) and the LED panel (or the aluminum heat sink), solution which allows the use of more efficient and cost effectively LED drivers, following boost or buck-boost topologies.
6.7 AC/DC SMPS LED Drivers
The AC/DC SMPS LED drivers follow the same three main circuit topologies described above, but they are more expensive and sophisticated than the DC/DC ones because, in the AC-to-DC conversion systems, an additional PFC (Power Factor Correction) sub-circuit is required, which increases by 30-50% the number of components and implicitly, the size and cost of the AC/DC LED driver, function of the block schematic topology chosen, respectively, “double stage” or “single stage”.
6.8 Double Stage LED Drivers
The Double Stage SMPS LED driver systems are the “state of the art topologies” in which a first stage AC/DC PFC sub-circuit (boost, typically) converts, under near unity power factor, the inputted unregulated AC Voltage into a pre-regulated outputted DC voltage, and a following second stage DC/DC PWM sub-circuit (buck, buck-boost or flyback) converts the inputted pre-regulated DC voltage into an outputted Regulated DC Voltage, while controlling, precisely, the LED stripes current amount, as well. The double stage system uses two integrated circuits (one PFC and one PWM) controllers, two MOSFET buffers and two oscillating inductors, besides 40-60 other lower cost parts, fact which increase, substantially its cost and size, with respect to the single stage solution.
6.9 Single Stage SMPS LED Drivers
The Single Stage SMPS LED driver systems are the “cost effective topologies” in which only one sub-circuit performs both, the PFC and the PWM functions, using only one integrated circuit, one MOSFET buffer transistor and one oscillating inductor, saving 20-50% of the circuit parts count, size and cost, with respect to the Double Stage topology, under lower performance.
More details related to the SMPS LED Drivers advantages and shortcomings will be presented hereinbelow.
7. Monolithic LED Driver Circuits
It will be appreciated that the monolithic LED drivers could be considered “the ideal LED drivers of the future”, because they are capable of reducing a 30-100 components SMPS LED driver circuit, down to only “one solid state component”, respectively down to just one microchip capable of driving LED stripes in a very safe and reliable CVCC manner, featuring top performance in AC circuits, as well, such as Eff>95%, PF>0.99 and A.THD<5%.
Additional grounds for designers to do their best to develop and promote, shortly, this very new technology into the worldwide market, consist in their amazingly small size (miniature surface mount chip which can fit in any small lamp or even inside of a LED or LED Array's package) and their “virtually unlimited life time” which will solve, at last, the main issue the SMPS drivers are facing right now.
The main shortcomings of conventional monolithic LED drivers are lower utilization factor, higher flickering coefficient and dependence on a specific number of LEDs per stripe, for any given supply voltage amount.
Nevertheless by considering on one hand, the very short time that has passed since this new technology has left the pioneer designers R&D bench and on the other hand, the endless potential advantage offered by these devices, chances are for the monolithic LED driver to become “the monolithic LED lamp retrofit” of the future, reaching top performances and a manufacturing cost lower than the manufacture cost of our conventional Edison bulb, today.
Therefore, the present specification provides only ten SMPS LED driver embodiments and twenty Monolithic LED embodiments.
More details related to the Monolithic LED Drivers advantages and shortcomings will be presented hereinbelow.
8. LED Drivers Comparison Criteria
For a fair evaluation with respect to the quality versus cost feature of each particular LED driver, versus other drivers provided by hundreds of power management product manufacturers, worldwide, first it is recommended to separate them in “similar drivers groups” and after that to set up suitable criteria of comparison.
Besides the very conventional boost, buck, buck-boost and isolated non isolated (single ground) flyback topologies mentioned above, there are many other options available for designers, for improving or optimizing a driver's performance, size and cost, by choosing the Continuous Mode, the Discontinuous Mode or the Critical Conduction Mode of operations, executed in a Fixed Frequency, Constant ON Time Variable Frequency, or Constant Off Time Variable Frequency manner, and therefore, it is not easy to make a direct comparison in such a hot market where, “revolutionary innovations” are advertised, worldwide, almost on a monthly basis.
The complexity of choices a circuit designer faces is endless and by considering the fact that the high power LED drivers industry has only about five years of competitive history, the common sense conclusions are:
a) there is no proven “ideal LED lamp retrofit” in the existing market, at this time.
b) there could be many other ways to design a LED driver circuit and sufficient room for improvements.
c) the only way to evaluate, fairly, the quality of a new LED driver circuit, is to compare it with several existing solutions operating in the same range of power and following the same (or similar) topology provided by the top experts of the power management industry.
An evenhanded comparison is supposed to be based on at least 14 key data arranged in a “Parts and Performance Chart” approach, providing sufficient information about the size, quality and cost features of each LED driver, such as:
1) Parts Count section, including the expensive parts amount (in parenthesis) shows the system complexity and provides indications of the circuit's size and cost.
2) Integrated Circuits section, including expensive opto-couplers (in parenthesis), shows the number of controller chips required by a particularly design.
3) Transistors section, including expensive FET transistors (in parenthesis), shows the number of transistors required by a particularly design.
4) Diodes section, including the more expensive bridge, Schottky and fast recovery (in parenthesis) shows the number of diodes required by a particularly design.
5) Capacitors section, including unreliable, bulky and expensive electrolytic capacitors (in parenthesis) shows the number of capacitors required by a particularly design.
6) Inductors section, including unreliable, bulky and expensive transformers (in parenthesis) shows the number of coils required by a particularly design.
7) Resistors section, including more expensive larger size high power current sense resistors (in parenthesis) shows the number of resistors required by a particularly design.
8) Efficiency section shows the driver's quality to put money back in its end user's pocket, offering more light but lower monthly electricity bill, than other drivers.
9) Power Factor showing the amount of overheat eliminated from the national power grid and environment.
10) A.THD showing the degree of pollution saved from the national power grid and environment (radio noise).
11) LED Stripes CCS section shows how many LED stripes a particularly LED driver can control in a very safe CVCC (constant voltage constant current) mode of operations.
12) Board Size section shows if the driver can fit or not in small or flat bulb retrofits, and could be Extra Large (EL), Large (L), Medium (M), Small (S) and Very Small (VS).
13) Total Cost section indicate the relative cost of the driver's parts and labor, estimated as Very High (VH), High (H), Medium (M), Low (L) and Very Low (VL).
14) Lifetime section shows the pre-estimated lifetime of a driver, function of the lifespan of its components, measures in years (yrs) of operations at 24 hours a day use, showing also the degree of hope the end user may have to recover partially, or in full, the much higher cost price he had to pay for this amazingly efficient but still fragile LED lamp retrofit (i.e., important feature and sales point).
Accordingly, the present specification provides a detailed description of the related art, created over the years by leading LED Driver designers.
Since the LED driver is a vital component of all LED lamp retrofits and therefore, in various embodiments, the present specification provides novel LED driver systems featuring low component count, smaller size, lower cost, longer lifetime and higher electrical performances than most of the high quality LED drivers, existing in the worldwide market.
In order to achieve this goal for each kind of LED lamp retrofit required by the existing market, the LED driver embodiments described herein provides one specific topology, such as boost, buck-boost or flyback, applied in a double stage or single stage manner and of course, using fixed or variable frequency techniques approach, for optimizing all the parameters involved in a high quality/low cost LED driver's design.
In the same light, several novel circuit embodiments are provided targeting high quality low cost monolithic LED drivers, have been included in this specification.
For a fair appreciation of the value, importance and/or immediate need of each improvement or novel system presented herein, each embodiment will be fully described and presented, comparatively, in accordance with the same 14 key factors mentioned above, with a very similar high quality LED driver solution, published in Datasheets, Application Notes or technical Magazines by companies having very good reputation in the worldwide power management industry, such as: Texas Instruments, Fairchild, Power Integrations, Maxim, Seoul Semiconductor, Linear Technology, Intersil, Exclara, Supertex, and others.
9. Related Art—SMPS LED Drivers
9.1 Double Stage Off-line Boost-Flyback Isolated SMPS—TI
A double stage off-line boost-flyback circuit example, suitable to the context of the present specification, is revealed in the Texas Instruments (TI) publication “SLUU341B” entitled “PR883: A300-W, Universal Input, Isolated PFC Power Supply for LCD TV Applications”, published in December 2008, capable of providing a constant output voltage of 24 V for loads up to 12 A at high performance complying with the power quality meeting the Energy Star requirements and the IEC standards. It achieves state of the art double stage circuit control methods including, as a first stage, a boost pre-regulator securing a near unity power factor in an off-line (85-265 Vrms) range of input voltage and, as second stage, an LLC resonant DC-DC isolated flyback converter. The control system design requires five integrated circuits, such as the UCC28061 for the first stage, the UCC25600 as well as two opto-couplers H11AV1A-M using the TL431AIDBV voltage reference for the second stage, and the UCC2813D-4 for an extra flyback converter, providing bias supplies to the entire system.
The most significant data of the SMPS circuit described above, collected from Table 1 (page 2) and Table 4 (pages 19, 20, 31) of the above-referenced TI publication are provided in the parts and performance chart shown below.
The SMPS circuit's performances specifications collected from Table 1 (page 2) and the components amount of each category, collected from Table 4 (pages 19, 20, 31) of the above-referenced TI publication, are summarized in Table 1, below.
TABLE 1Double Stage Off Line Isolated Boost-Flyback Driver-TexasInstruments1Parts Count (expensive)136(32) 2Integrated Circuits-(opto-5(2)couplers)3Transistors-(FETs)8(5)4Diodes-(bridge & fast14(9)recovery)5Capacitors-(electrolytic)50(11) 6Inductors-(Transformers)3(3) 7Resistors-(high power)56(2)8.Efficiency (typ.)   87%9Power Factor0.95(typ.)10 A. THD (typ.)<10%11 LED Stripes CCS112 Board SizeVL13Cost (total)VH14 Lifetime (years)3
The main advantage of this double stage SMPS circuit consist in the fact that provides I/O circuits isolation and the first stage (boost) converts the unregulated AC input voltage into a regulated (390V) DC voltage, so the second stage (flyback) will always have sufficiently high supply voltage amount for delivering to its load a precisely regulated DC voltage having very small ripples.
The main shortcomings of this circuit are:
Too many parts count.
Too many and expensive integrate circuits.
Too many expensive UIF diodes.
Too many bulky and unreliable electrolytic capacitors.
Too many bulky, unreliable and expensive inductors.
Very Large size of the driver board which does not allow its use in small size devices.
Very high cost solution, incompatible to the excepted cost of LED lamp retrofits operating in small and medium power range.
In contrast, the various embodiments disclosed provide several solutions to solve all the above mentioned inconveniences, including a novel double stage system embodiment and four “pseudo double stage” system embodiments capable to reach similar performances (Eff>87%, PF>0.99%, A.THD<10%) while reducing the parts count, size and cost in a ratio of 40-60% with respect to this particularly LED driver solution.
9.2 Double Stage SEPIC/Buck LED Driver—Supertex
A double stage SEPIC/buck LED Driver circuit example, suitable to the context of the disclosed embodiments, is shown in the Supertex, Inc. “HV9931DB2v1” chip presentation folder regarding a “LED Driver Demo Board Input 230 VAC//Output 350 mA, 40V” capable of providing a constant output voltage up to 40V to a 14 W load at very good performance. It achieves decent quality double stage circuit control methods including, as a first stage, a buck-boost (SEPIC) pre-regulator securing a near unity power factor in a range of 200-265 Vrms input voltage and, as second stage, a non isolated pack current limited Constant Off Time (COT) buck converter operating in a continuous conduction mode (CCM). The control system design requires only one MOSFET transistor and controller IC, the HV9931LG for both, first and second stages, having up 30% inductor current ripple.
The most significant data of the LED driver circuit described above, collected from the HV9931LG chip presentation folders are provided in the parts and performance chart shown below in Table 2.
TABLE 2Double Stage Non-Isolated Off Line SEPIC/Buck LED Driver-Supertex1Parts Count63(9)2Integrated Circuits-(opto-couplers)1(0)3Transistors-(FETs)5(1)4Diodes-(bridge & fast recovery)13(6)5Capacitors-(electrolytic)15(0)6Inductors-(Transformers)4(0)7Resistors-(high power)25(2)8Efficiency (typ.)  87%9Power Factor (typ.)0.9510A. THD (typ.)<10%11LED Stripes CCS112Board SizeM13Cost (total)M14Lifetime (years)3
The main advantages of this particular converter circuit is that it uses only one MOSFET transistor and one integrated circuit to control both stages, does not use electrolytic capacitors and eliminates the need for opto-couplers or differential sensing voltage amplifiers by using the SEPIC buck-boost configuration which allows the controller IC to sense the LEDs current with respect to a common ground.
The main shortcomings of this circuit are:
No Isolation between the input and the output circuits.
Too many parts count.
Too many and bulky coils
Too many and expensive UIF diodes.
High current ripples of the inductor.
Medium size of driver board which does not allow its use in very small size LED lamp retrofits.
Relatively high cost for small range power retrofits.
The SEPIC capacitor (E31) is bulky, expensive and it may lead to instability, in time, at high frequency AC current, shortening the retrofit's lifespan.
The present specification provides several embodiments to overcome the above mentioned shortcomings, including a novel double stage system embodiment and four “pseudo double stage” system embodiments capable to reach similar performances (Eff>87%, PF>0.99%, A.THD<10%) while reducing the parts count, size and cost in a ratio of 25-30% with respect to this particularly LED driver solution.
9.3 Boost Single Stage Off Line LED Driver—Intersil
A boost single stage LED Driver circuit example, suitable to the context of the present specification, is illustrated and described in the Intersil application note AN1387.0 entitled “White LED Driver Circuits for Off-Line Applications using Standard PWM Controllers”, published on Feb. 12, 2009 for the use of its proprietary ISL6445IAZ-TK integrated circuit (IC), which is a capable of operating in three different topologies, such as Single Stage Boost, Single Stage (SEPIC) Buck-boost and Single Stage Flyback LED driver circuits. This single stage boost LED driver application illustrated in FIG. 12 of the above-reference Intefrsil publication. Detailed Boost Converter Schematic (page 11), of the publication, is a very conventional one, using the ISL6445IAZ-TK chip as a PWM/PFC controller and a second dual operational amplifier LM358 (Texas Instruments) chip for controlling, differentially, the voltage and current across the LEDs, with respect to a high precision micro-power shunt voltage reference chip LM4041 (Texas Instruments). The circuit is capable of reaching near unity power factor, operating in critical conduction mode (CrCM) and delivering an output voltage of 250 Vdc, when is supplied at 90-120 Vac (Japan and USA), being designed for high power LED panels using over 50 LEDs per one stripe, and it requires an additional operational amplifier for securing the constant current of each additional LED stripe.
The most significant data of the LED driver circuit described above collected from the ISL6445IAZ-TK chip presentation folders are summarized in Table 3 below.
TABLE 3Boost Single Stage Off Line LED Driver-Intersil1Parts Count (expensive)42(11) 2Integrated Circuits-(opto-3(0)couplers)3Transistors-(FETs)2(1)4Diodes-(bridge & fast13(6)recovery)5Capacitors-(electrolytic)11(3)6Inductors-(Transformers)2(0)7Resistors-(high power)19(1)8Efficiency (typ.)  90%9Power Factor>0.9(typ.)10A. THD (typ.)<20%11LED Stripes CCS112Board SizeM13Cost (total)L14Lifetime (years)3
The main advantage of this particular single stage boost converter circuit is the higher efficiency it provides over all the other topologies, very important feature in high power application.
The main shortcomings of this circuit are:
a) No I/O circuits isolation.
b) Too many parts for a single stage boost converter.
c) Three integrated circuits instead of one.
d) The ISL6445IAZ-TK chip supply circuit is too large and expensive, consisting in a high voltage series regulator, including a high voltage (350V) transistor, a zener diode, and four resistors.
e) Requires unreliable electrolytic capacitors.
f) CCS for only one LED stripe.
g) Minimum 50 LEDs per stripe, at 120 Vac supply.
Various embodiments according to the present specification provide several solutions to solve all the above mentioned inconveniences, including a novel boost single stage system embodiment capable to reach better performances (Eff>93%, PF>0.99%, A.THD<10%) while reducing the parts count, size and cost in a ratio of 15-20% with respect to this particularly LED driver solution.
9.4 Buck-Boost S. Stage LED Driver—Supertex Vs. UTC
A Buck-boost single stage low cost LED Driver circuit example, suitable to the context of the present specification, is shown in the Supertex, Inc. “HV9921” chip presentation folder regarding its minimum parts “3-Pin Switch-Mode LED Driver IC” capable of providing a constant output current of 20 mA to LED stripe despite an extremely large (85-264 Vrms) variation of the AC supply voltage. This was the most simple and low cost DC/DC LED driver, however, because it uses the COT (constant off time variable frequency) mode of operation, in AC/DC applications it has serious problems with the PF and A.THD parameters. For solving the PF and A.THD issues in the AC applications of the HV9921 chip, Supertex has recommended the use of a low cost passive PFC solution, consisting in a precisely calculated LC filter (one coil two capacitors) and eventually, Supertex has introduced its upgraded chip HV9931LG, described above, which was able to provide near unity power factor (PF=0.98) in a double stage topology.
The Chinese designers have followed up, shortly, this very low cost solution, advertising similar solution using the capabilities of a new generation of affordable eight pin COT driver chips, including the QX9910, provided by QXMD and the UCT4390, provided by UCT.
The variable frequency-constant off time single stage buck-boost LED driver circuit advertised by UCT in the UCT4390 chip's datasheets features reasonable performance in AC applications by using a conventional “valley fill filter” passive PFC circuit, consisting of two capacitors coupled in series across the output of the supply rectifier bridge, having a first rectifier diode coupled between them and two extra rectifier diodes, coupled from the anode and the cathode of the first rectifier diode to the positive and the negative outputs of the bridge rectifier, in such a manner for the capacitors to have a series charging circuit and a parallel discharging circuit. Since the equivalent capacitance of two equal valued capacitors coupled in series is half of each capacitor and in parallel circuit is double of each capacitor, the power factor is significantly improved (typically 0.85-0.9), especially if additional low pass (or EMI) filters, consisting of one double coil and two capacitors, are included into the AC supply circuit.
The most significant data of the LED driver circuit described above, collected from the UTC4390 chip presentation folders are summarized in Table 4 below.
TABLE 4Buck-boost Single Stage Off-line Low Cost LED Driver-UTC1Parts Count3210 2Integrated Circuits-(opto-1(0)couplers)3Transistors-(FETs)2(2)4Diodes-(bridge & fast11(1)recovery)5Capacitors-(electrolytic)10(5)6Inductors-(Transformers)2(1) 7Resistors-(high power)6(2) 8.Efficiency (typ.)  80%9Power Factor0.85(typ.)10A. THD (typ.)<30%11LED Stripes CCS112Board SizeM13Cost (total)L14Lifetime (years)2
The main advantages of this particular constant off time LED driver circuit are: low component count, medium size board and low total manufacturing cost, fact which made China the #1 provider of fluorescent LED lamps retrofits in the entire South Asia's market and a major competitor in the worldwide market.
The main shortcomings of this circuit are:
Short lifetime because of the electrolytic capacitors.
No Isolation between the input and the output circuits.
Too many bulky and unreliable electrolytic capacitors.
The need for 2-3 EMI filters for reaching PF=0.9.
No voltage control over the LED stripe.
Supplies the IC controller via a second FET transistor.
Bulky coils and capacitors increase the board size.
Relatively low performance versus other solutions.
The present specification provides several embodiments to overcome the above mentioned shortcomings, including novel and lower cost COT LED driver circuit embodiments used with valley fill filters and/or used as second stage DC/DC converters in low cost high power factor (PF=0.99) double stage LED lamp retrofit driver circuit embodiments.
9.6 Buck-Boost Single Stage LED Driver—PI
A buck-boost single stage LED driver circuit example, suitable to the context of the present specification, is shown in the Power Integrations (PI) “Constant Current <2% Regulation) Non-Isolated Buck-Boost, Power Factor Corrected 18 W LED Driver Using LinkSwitch—PH LNK419EG” design example report of Dec. 8, 2011.
This driver circuit is capable to provide a 200V voltage and 90 mA current+/−30% ripple DC output in an AC supply range of 90-265V.
The LNK419EG controller chip includes the MOSFET buffer and is capable of limiting converter output current maintaining a near unity power factor and does not use opto-couplers and operational amplifiers for sensing the output current, but a 11 parts feedback circuit including a voltage shunt regulator chip LMV431AIMF a high voltage transistor FMMT560, 2 diodes, 5 resistors and 2 capacitors
The most significant data of the LED driver circuit described above, collected from the LNK419EG chip presentation folders are summarized in Table 5 below.
TABLE 5Buck-boost Single Stage Off-line LED Driver-Power Integrations1Parts Count (expensive)37(7)2Integrated Circuits-(opto-1(0)couplers)3Transistors-(FETs)1(0)4Diodes-(bridge & fast7(4)recovery)5Capacitors-(electrolytic)10(2) 6Inductors-(Transformers)3(0)7Resistors-(high power)15(1)8.Efficiency (typ.)  89%9Power Factor>0.92(typ.)10A. THD (typ.)<30%11LED Stripes CCS112Board SizeS13Cost (total)L14Lifetime (years)3
The main advantages of this particular buck-boost converter circuit are: the controller chip LNK419EG includes the large and expensive MOSFET buffer, is capable to control the output current while keeping the power factor near unity and does not use expensive opto-couplers and operational amplifiers for current feedback but lower cost passive parts and a bipolar transistor.
The main shortcomings of this circuit are:
No Isolation between the input and the output circuits.
The current feedback requires too many parts (11).
Transistors are instable with variation of temperature.
High current ripples of the output current (30%).
Too many and expensive UIF diodes.
Relatively high cost for small range power retrofits.
The present specification provides several embodiments to overcome the above mentioned shortcomings, including a single stage single ground buck-boost system embodiment capable of reaching better performances (Eff>88%, PF>0.99%, A.THD<10%) while reducing the parts count, size and cost in a ratio of 20-35% with respect to this particularly LED driver solution.
9.3 Flyback S. Stage Non-Isolated LED Driver—Intersil
A flyback single stage LED Driver circuit example, suitable to the context of the present specification, is illustrated and described in the Intersil application note AN1387.0 entitled “White LED Driver Circuits for Off-Line Applications using Standard PWM Controllers”, published on Feb. 12, 2009 for the use of its proprietary ISL6445IAZ-TK integrated circuit (IC), which is a capable to operate in three different topologies, such as Single Stage Boost, Single Stage (SEPIC) Buck-boost and Single Stage Flyback LED driver circuits. This single stage non-isolated flyback LED driver application illustrated in FIG. 14 of the above-referenced Intersil publication. “Detailed Flyback Converter Schematic” (page 13) is a very conventional one, using the same components as the Intersil boost converter described above, respectively the ISL6445IAZ-TK chip as a PWM/PFC controller and a dual operational amplifier LM358 chip for controlling, differentially, the voltage and current across the LEDs, with respect to a high precision micro-power shunt voltage reference chip LM4041. The main differences with respect to the boost circuit consists of the fact that the flyback inductor is a two coils transformer and therefore, a three parts conventional snubber circuit, consisting of one diode, one resistor and one capacitor, has been added in the drain circuit of the MOSFET buffer (Q1), for high voltage limitation.
The circuit is capable of reaching near unity power factor, operating in critical conduction mode (CrCM) and delivering an output voltage, usually, lower than the input AC voltage (90-260 Vac) having the capably to supply one stripe of one or more LEDs connected in series and requiring an additional operational amplifier for securing the constant current of each additional LED stripe.
The most significant data of the flyback LED driver circuit described above, collected from the ISL6445IAZ-TK chip presentation folders is summarized in Table 6 below.
TABLE 6Flyback Single Stage Off-line Non-Isolated LED Driver-Intersil1Parts Count (expensive)53(13) 2Integrated Circuits-(opto-couplers) 3(0)3Transistors-(FETs)2(1)4Diodes-(bridge & fast14(7)recovery)5Capacitors-(electrolytic)12(3)6Inductors-(Transformers)2(1)7Resistors-(high power)20(1)8.Efficiency (typ.)  80%9Power Factor>0.9(typ.)10A. THD (typ.)<20%11LED Stripes CCS112 Board SizeM13Cost (total)M14Lifetime (years)3
The main advantage of this particular single stage non-isolated flyback converter circuit consists of its very safe and accurate control of the LED current and voltage, via the two operational amplifiers included in the LM358 and the precise reference provided by the LM4041 voltage shunt regulator, despite large variations of the ambient temperature.
The main shortcomings of this circuit are:
a) No I/O circuits isolation.
b) Too many parts for a single stage boost converter.
b) Three integrated circuits instead of one.
c) Too many parts (6) used for the controller chip supply.
d) Requires bulky and unreliable electrolytic capacitors.
e) CCS for only one LED stripe.
f) Higher cost than other similar topology solutions.
The present specification provides several embodiments to overcome the above mentioned shortcomings, including a novel non-isolated and isolated single stage LED driver system embodiment, capable of reaching better performances (Eff>88%, PF>0.99%, A.THD<10%) while reducing component count, size and cost in a ratio of 30-50% with respect to this particularly LM4041 LED driver solution.
9.7 Flyback Single Stage Isolated LED Driver—Fairchild
A flyback single stage isolated LED driver circuit example, suitable to the context of the present specification, is shown in the Fairchild application note AN-9737 entitled “Design Guide for Single-Stage Flyback AC-DC Converter Using FL6961 for LED Lighting” presenting a 16.8 W power factor corrected LED driver, delivering an output of 24V/0.7 A and featuring soft-starting and CVCC feedback for a very accurate (cycle-by-cycle) and reliable control of the LED stripe's V/I parameters.
The FL6961 controller chip operates in constant on-time (variable off time) and CrCM (critical conduction mode, at the boundary between the discontinuous and continuous mode of operation) for securing a good power factor while controlling also the LEDs maximum voltage and current. The FL6961 chip supply voltage is obtained via an additional winding added to the flyback transformer and the output voltage/current feedback is conventional, using the KA358 dual error amplifier, the KA431 voltage shunt regulator as reference and the FOD817 opto-coupler, for securing the input/output circuits isolation.
The most significant data of the LED driver circuit described above, collected from the LNK419EG chip presentation folders is summarized in Table 7 below.
TABLE 7Flyback Single Stage Off-line Isolated LED Driver-Fairchild1Parts Count (expensive)47(17) 2Integrated Circuits-(opto-4(1)couplers)3Transistors-(FETs)1(1)4Diodes-(bridge & fast9(4)recovery)5Capacitors-(electrolytic)13(3)6Inductors-(Transformers)4(1)7Resistors-(high power)16(7)8.Efficiency (typ.)  82%9Power Factor>0.9(typ.)10A. THD (typ.)<20%11LED Stripes CCS112Board SizeS13Cost (total)M14Lifetime (years)3
The main advantages of this particular flyback converter circuit are: uses only one chip to control the output current and voltage while keeping the power factor near unity, uses precise and reliable voltage shunt regulator and operational amplifiers for voltage and current feedback and uses opto-coupler for securing the input/output circuits isolation.
The main shortcomings of this circuit are:
Many parts count.
Expensive V/I feedback circuit.
Higher cost than other isolated flyback solutions.
CCS for only one LED stripe.
Larger Vout ripples than double stage solutions.
The present specification provides several embodiments to solve the above mentioned shortcomings including single stage isolated flyback and double stage multi-columns LED driver system embodiments capable of reaching better performance (Eff>85%, PF>0.99%, A.THD<10%) while reducing component count, size and cost in a ratio of 20-35% with respect to this particularly LED driver solution.
9.8 Flyback Single Stage Isolated LED Driver—PI
A flyback single stage isolated LED driver circuit example, suitable to the context of the present specification, is shown in the Power Integrations (PI) RDR-193 application entitled “Reference Design Reports for s High Efficiency (>81%), High Power Factor (>0.9) TRIAC Dimmable 7W LED Driver Using LinkSwitch—PH LNK403EG” presenting a 7 W power factor corrected LED driver, delivering an output of 21V/0.33 A in a supply range of 90-265 VAC.
The LNK403EG controller chip operates in CCM (continuous conduction mode of operations) and the output current regulation is sensed entirely from the primary side of the flyback transformer eliminating the need of the expensive opto-coupler, operational amplifier and voltage shunt regulator connected, usually, in the flyback secondary side.
The most significant data of the LED driver circuit described above collected from the LNK403EG chip presentation folders is summarized in Table 8 below.
TABLE 8Flyback Single Stage Off-line Isolated LED Driver-PowerIntegrations1Parts Count (expensive)50(13) 2Integrated Circuits-(opto-1(0)couplers)3Transistors-(FETs)3(1)4Diodes-(bridge & fast12(5)recovery)5Capacitors-(electrolytic)12(5)6Inductors-(Transformers)3(1)7Resistors-(high power)19(1)8.Efficiency (typ.)81%9Power Factor>0.9(typ.)10A. THD (typ.)<20%11LED Stripes CCS112Board SizeS13Cost (total)M14 Lifetime (years)3
The main advantages of this particular flyback converter circuit are: uses only one chip to control the output current and voltage while keeping the power factor near unity, the MOSFET buffer is included in the controller chip and senses the LEDs current from the primary section of the flyback transformer for securing the input/output circuits isolation and eliminating the need for the expensive conventional current feedback circuit.
The main shortcomings of this circuit are:
Many parts count.
Too many (5) electrolytic capacitors.
Requires an ultra fast diode in the buffer circuit.
Higher cost than other isolated flyback solutions.
Relatively low Eff and PF for high cost.
CCS for only one LED stripe.
Larger Vout ripples than double stage solutions.
The present specification provides several embodiments to solve the above mentioned shortcomings, including a single stage isolated flyback and a double stage multi-columns LED driver system embodiments capable to reach better performances (Eff>88%, PF>0.99%, A.THD<10%) while reducing the parts count, size and cost in a ratio of 20-25% with respect to this particularly LED driver solution.
9.9 Flyback Single Stage Isolated LED Driver—LT
A flyback single stage isolated LED driver circuit example, suitable to the context of the present specification, is shown in the Linear Technology (LT) demo manual DC1744A entitled “LT3799 Offline Isolate Flyback LED Driver with PFC” presenting a power factor corrected LED driver capable to deliver 4-100 W to an LED display in a supply range of 90-265 VAC.
The LT3799 controller chip operates in critical conduction mode (CrCM, at the boundary between the discontinuous and continuous mode of operation, similar to the Fairchild's FL6961, presented above) for securing a good power factor while controlling also the output current regulation (similar to the PI's LNK403EG) entirely from the primary side of the flyback transformer eliminating the need of the expensive opto-coupler, operational amplifier and voltage shunt regulator connected, usually, in the flyback secondary side.
The most significant data of the LED driver circuit described above, collected from the LT3799 chip presentation folders is summarized in Table 9 below.
TABLE 9Flyback Single Stage Off-line Isolated LED Driver-LinearTechnology1Parts Count (expensive)41 (9)2Integrated Circuits-(opto-1(0)couplers)3Transistors-(FETs)1(1)4Diodes-(bridge & fast recovery)6(5)5Capacitors-(electrolytic)11 (1)6 Inductors-(Transformers)4(1)7 Resistors-(high power)18(1) 8.Efficiency (typ.)>80%9Power Factor>0.9(typ.)10A. THD (typ.)<20%11 LED Stripes CCS112Board SizeS13Cost (total)VH14Lifetime (years)3
The main advantages of this particular flyback converter circuit are: uses only one chip to control the output current and voltage while keeping the power factor near unity and senses the LEDs current from the primary section of the flyback transformer, eliminating the need for the expensive conventional error amplifier feedback circuit and opto-coupler for securing the I/O circuits isolation, using only one electrolytic capacitor.
The main shortcomings of this circuit are:
LT's driver solutions and parts are very expensive.
Relatively low Eff and PF for very high cost.
CCS for only one LED stripe.
Larger Vout ripples than double stage solutions.
The present specification provides several embodiments to solve the above mentioned shortcomings, including a single stage isolated flyback and a double stage multi-columns LED driver system embodiments capable to reach better performances (Eff>88%, PF>0.99%, A.THD<10%) while reducing component count, size and cost in a ratio of 20-25% with respect to this particularly LED driver solution.
10. Related Art—Monolithic LED Drivers
10.1 Low Dissipation Controllable Electron Valve
A patent entitled “Low Dissipation Electron Valve For Controlling Energy Delivered To A Load And Method Therefore” was issued on Jan. 28, 1997, as U.S. Pat. No. 5,598,093, where the inventor, Beniamin Acatrinei (author of the present specification) has revealed a new and original way of controlling the transfer of the electrical energy from an AC generator to a load by using the capabilities of a novel and extremely versatile “electron valve” called the “Benistor”, name coming from its “Blockade of Electrical Network” capability leading to an original “SSCVCC” (self-switching constant voltage constant current) mode of operation.
Unlike the previously invented solid state electron valves, such as the “transistor” and “thyristor” (SCR—Silicon Control Rectifier), the Benistor is able to control a high power rectified AC sine wave and deliver a suitable electrical supply to any kind of loads (including LEDs) in linear, switching and/or SSCVCC operations manner, without requiring an external driver circuit (similar to the transistor) and also, without dissipating significant energy internally (similar to the thyristor).
By using this original SSCVCC mode of operation, the Benistor eliminates the needs for coils and capacitors used in most conventional AC/DC or DC/DC converters and, in circuits where it is coupled, directly, between a bridge rectifier (“BR”) and a load, the Benistor delivers to its load a continuous (by switching ON) or interrupted (by switching OFF) DC supply, in such a manner as to always keep the voltage across the load within pre-established limits, despite large variations of its input supply (BR's output) voltage.
The Benistor can operate in a linear manner, as well, for keeping the load current within pre-established limits, although this mode of operation is not as efficient as the self-switching one.
For being able to perform this complex SSCVCC mode of operations, the “conventional” Benistor relies on seven in/out terminals, such as:
a “Vin” (voltage input) input power terminal coupled to the BR's positive output,
a “CE” (common electrode) terminal coupled to the BR's negative output (or ground, “GND”),
a “Vout” (voltage output) output power terminal coupled across the load, jointly with the CE terminal,
an “ON-OFF” voltage control input terminal which turns ON an internal switch between Vin and Vout when Vin<Von-off and turns OFF the internal switch between Vin and Vout when Vin>Von-off
an “OFF-ON” voltage control input terminal which does the same self-switching job but in opposite phase with respect to the ON-OFF input terminal.
a “CC+” voltage control input terminal operating “in positive phase” with the output, respectively the current delivered by Vout increases when the amount of the voltage applied a the CC+ terminal increases, and
a “CC−” terminal which operates opposite than CC+.
This extremely versatile device has its own electrical symbol, similar to a vacuum tube and multi-terminal transistor devices, and does not require external components but only fixed or variable DC voltage applied to its terminals, for operating like a transistor, thyristor, operational amplifier, window comparator, CCS (constant current sink), VCS (voltage controlled switch), and of course, similar to the conventional complex transistors circuits, “Benistors complex circuits” could be achieved, where two or more Benistors could be connected in very many configurations, such as: series, parallel, mirror, totem pole, push-pull, etc.
Despite the fact that the Benistor's internal block schematic circuit appears sophisticated, especially because of its seven terminals, minimum parts Benistors may have as few as three terminals (like a transistor) and internally, only a two transistors circuit, looking similar to the conventional thyristor's equivalent circuit (i.e., NPN and PNP transistors coupled mutually, base-collector) with one difference being the base of the NPN transistor is “in air” (not connected) for allowing many other ways to connect the two transistors with the external circuit and of course, to make available many additional applications.
Because of its amazing simplicity and versatility, on Jul. 6, 1998 the Benistor achieved the “Cover Feature Story” award of Electronic Design Magazine, a very good reputation technical publication, where the Benistor was called “The Fourth Element”, which appeared in the worldwide electronic industry after the only three other “electron valves” created over the last one hundred years, such as the vacuum tube, the transistor, and the thyristor.
Unfortunately, at that time there were no “Ultra Bright White LED” and no “LED Lamp Retrofits” applications where the Benistor could confirm its special capabilities.
Therefore, in accordance with the present specification, several embodiments are provided that employ the Benistor's concept for achieving low cost, small size, no coils or capacitors and, eventually, no external parts monolithic LED driver, the “chip” which could be the main component of future “ideal” LED lamp retrofit devices.
10.2 System for Providing AC Line Power to Lighting Devices—Exclara
A patent application entitled “Apparatus, Method And System For Providing AC Line Power To Lighting Devices” has been published on Dec. 9, 2010, as the US Patent Application Publication No. 2010/0308739 A1 (Inventors: Shteynberg et. al., Assignee: Exclara, Inc.) revealing several LED driver converter circuits comprising no reactive components, but only solid state components such as transistors and resistors, parts which can be integrated into a “driver chip”, eventually.
Exclara, Inc. is one of the active “pioneers” in the LED lighting industry which devoted a significant part of its product development course for eliminating completely the unreliable, bulky and expensive reactive components, such as coils and capacitors, targeting a “monolithic LED driver” device which could be executed fast and cost effectively in a silicon foundry, for reducing the size and cost of the LED lamp retrofits and, more importantly, to increase the maximum lifetime of these efficient devices, since the solid state devices feature a “virtually unlimited lifetime”, while the electrolytic capacitors “get dry”, and compromise the lifespan of the entire LED lamp in just about 2 years of use, at 24 hours per day.
The embodiments presented in the above mentioned patent application publication, show a solid state “Controller” circuit features a relatively complex block schematic diagram, comprising a “Digital Logic Circuit” which activates or deactivates several “Switch Driver” devices which, external to the main Controller circuit, connect or disconnect several LED stripes included in a rectified AC supply circuit, in specific sequences determined by several other sub-circuits, such as: A/D Converters, Sync Signal Generator, Vcc Generator, Over Voltage Detector, Under voltage detector, Power On Reset, Memory and a Clock sub-circuit which establish the sequences timing, respectively the precise time when each Switch Driver connects or disconnects its designated LED stripe.
Each Switch Driver is equipped with a power MOSFET transistor, controlled in the gate by a fast driver including a comparator followed by a push-pull buffer, in order to increase the commutation speed and, implicitly, to decrease the On-Off transit time dissipation of each Switch Driver's power MOSFET transistor.
Eventually, by means of several voltage and current sensors input compared with internal voltage references and/or the logic data existing in the Memory sub-circuit, following a set of instructions shown in FIG. 22 of the above mentioned patent application publication, the Controller circuit connects, progressively, the LED stripes in such a manner, that when the amount of the voltage delivered by the bridge rectifies reaches its peak value (i.e., 170V for 120 Vrms line used in USA), all LED stripes are to be connected in series, when the AC supply voltage reaches its half value, only half of the LED stripes are to be connected and, finally, when the AC supply voltage decays down to 20-30V, then only one LED stripe is to be connected to the power line.
In this way, the controller is able to limit the LED current in 4 or more steps, so the current shape of the LED lamp retrofit device will appear like a “pyramid”, of 4 or more “square waves” positioned one on top of the other, based on how many Switch Drivers have a specific controller chip, and because the LEDs current increases proportionally with the AC supply voltage amount, the driver can reach a power factor parameter of over 0.9, in accordance to the Department of Energy and Energy Star's latest directives.
The first LED driver chip, “EXC100” introduced in the market by Exclara is presented by a LED lamp retrofit manufacturer, Everlight (www.everlight.com) under the title “Everlight HV LEDs Driving Note” which provides the schematic diagram, electrical specs and the device's current versus voltage shape, showing that only three LED stripes are used, for retrofits operating in the 4-10 W power range.
The most significant data collected from Everlight's web site regarding Exclara's monolithic LED driver chip, the EXC100, is summarized in Table 10 below.
TABLE 10System For Providing AC Line Power To Lighting Devices-Exclara1Parts Count (expensive)10 (0)2Integrated Circuits-(opto-1(0)couplers)3Transistors-(FETs)0(0)4Diodes-(bridge & fast recovery)0(0)5Capacitors-(electrolytic)0(0)6Inductors-(Transformers)0(0)7Resistors-(high power)9(0)8.Efficiency (typ.)  85%9Power Factor  0.95(typ.)10A. THD (typ.)<20%11LED Stripes CCS412Board SizeVS13Cost (total)VL14Lifetime (years)  5+
The main advantages of this particular monolithic LED driver circuit are: high performance, less parts count (10), very low size, very low cost and over 5 years lifetime.
As a brief comparison with the conventional SMPS driver solutions, the EXC100 chip's cost is $1.39/unit and the LT3799 cost is $2.70/unit, a chip which requires 40 additional parts and labor for its driver board and eventually, the LED lamp retrofit using the EXC100 has good chances to operate 2-3 years longer than the other.
The main shortcomings of this circuit are:
Very sophisticated internal architecture of the chip.
Up to 40 pin package, because of many A/D grounds.
Nine external resistors.
Square wave instead of sine wave current shape.
Very sophisticated design implementation calculations.
Visible flicker at low power and when dimmer are used.
The present specification provides several embodiments to solve the above mentioned shortcomings, including several monolithic LED driver system embodiments capable to reach higher performances (Eff=93%, PF=0.996%, A.THD=6%) while reducing the parts count down to only “one part”, respectively a lower size chip featuring only 8 pin package, extremely simple internal architecture and lower manufacturing cost in comparison to this particularly monolithic LED driver solution.
10.2 Linear LED Driver for Fluorescent Lighting Retrofits
A News Release presentation document entitled “New Sequential, Linear LED Drivers From Supertex Ideal For Fluorescent Tube Lighting Retrofits” has been published on Apr. 3, 2012 by Supertex, Inc., which is a recognized leader in high voltage analog and mixed integrated circuits (ICs), for introducing CL8800 and CL8801, sequential, linear LED drivers designed to drive long strings of low cost, low current LEDs in solid-state replacements for fluorescent tubes, incandescent bulbs and CFL bulbs. Both ICs minimize driver circuit component counts, requiring just four or six resistors and a diode bridge in addition to the IC.
The CL8800 has been designed for 230 VAC input and the CL8801 for 120 VAC input, and none of them requires coils or capacitors in the external circuit and, except for four additional components for transient protection, there is no need even for the typically used EMI filter since the two ICs do not use high frequency switching current techniques but only multi-stage linear regulators.
Several schematic diagrams exposed in the CL800 datasheets folder show that the Supertex new monolithic LED driver chip's pin-out configuration, functionality and LED stripe design calculations are almost identical to the Exclara's EXC100 controller chip, described above.
The most significant data collected from the Supertex CL8800 chip's datasheets is summarized in Table 11 below:
TABLE 11Linear LED Driver For Fluorescent Lighting Retrofits-Supertex1Parts Count (expensive)7(0)2Integrated Circuits-(opto-couplers)1(0)3Transistors-(FETs)0(0)4Diodes-(bridge & fast recovery)0(0)5Capacitors-(electrolytic)0(0)6Inductors-(Transformers)0(0)7Resistors-(high power)6(0)8.Efficiency (typ.)  90%9Power Factor (typ.)>0.9    10A. THD (typ.)<10%11LED Stripes CCS612Board SizeVS13Cost (total)VL14Lifetime (years)  5+
The performance shown in Table 11 looks a bit better than Exclara's shown in Table 10, and the cost/unit is higher ($2.38). However, since no patent application of Supertex Inc. has been published yet, and externally, the CL8800 circuit looks almost identical to the EXC100 circuit, the advantages and shortcomings related to this new monolithic LED driver solution are, more likely, very similar to ones presented above, for the Exclara EXC100 controller chip.
11. Conclusions
At this time, there are already hundreds of different LED Lamp retrofits available on the worldwide market for replacing all conventional incandescent, halogen, fluorescent, and sodium lamps. However, it will take some time until a few retrofit solutions will replace, rapidly the conventional lamps because of the cost versus quality and lifetime issues associated with these new devices.
Power management industry experts overwhelmingly agree that the LEDs are the “ideal light sources” of the future. However, similar to a “sodium lamp” which cannot provide “bright and efficient light” without “sodium”, a LED lamp retrofit cannot provide “good quality light” without a LED driver, and, with respect to this device's quality versus cost matters, there are hundreds of different concepts, opinions, and solutions, provided by the worldwide power management industry experts.
On one hand, we have the US and European experts providing “high quality, high reliability, but high cost LED drivers” and, on the other hand, we have the South Asian experts providing “reasonable quality, less reliability, but very low cost LED drivers” and, therefore, the market does not have yet “the ideal device”, which logically cannot be anything else but a “low cost, high performance, long lifetime LED lamp retrofit” apparatus which is, actually, the main subject of the present specification.
As presented above, the SMPS LED drivers and the Monolithic LED drivers have advantages but also many shortcomings, and, because of that, several embodiments referred to novel LED driver systems, whether or not they employ coils and capacitors, have been included in the present specification.
Therefore, an urgent need exists for low cost high quality LED lamp retrofits having fewer, smaller, or even no electrolytic capacitors, fewer, smaller, or even no coils, higher efficiency, higher power factor, low harmonic distortions, and lower total manufacturing cost, for replacing safely, shortly, and easily, all the existing obsolete conventional lamps, in such a manner for the end users to benefit of more light paying lower electricity bill, getting longer utilization time and lower total cost associated to each LED lamp retrofit, purchased.